1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to a method of adjusting a power of a forward link signal.
2. Background of the Related Art
Generally, in a radio communication system, a power control of a physical channel for transmitting data is performed to maintain the communication quality of the transmitted data. The power control method is classified into an outer loop power control and an inner loop power control.
In the outer loop power control method, a receiving end measures the frame quality of the present data frame of the physical channel subject to the power control. Also, the receiving end adjusts a target value of a ratio of a received signal to noise signal power ratio according to the degree of the measured frame quality. Herein, the frame generally means a unit of data transmitted through the physical channel. For example, it may be a unit for performing one error correction encoding.
In the inner loop power control method, the receiving end calculates a ratio of the received signal to noise signal power during a transmission period of the present power control group (PCG) of the physical channel subject to the power control. Also, at this time, the receiving end compares the ratio of the received signal to noise signal power for the present PCG with the target value, and commands a control (for example, transmission power increasing/decreasing command) of a transmission power of the physical channel according to a result of comparison.
A transmitting end performs a specified operation with respect to the transmission power of the physical channel based on the command for the power control. Herein, the PCG indicates the power control unit, and in case of the power control with 800 Hz, the length of one PCG becomes 1/800(=1.25 msec).
However, the conventional inner loop power control has the following problems.
If the transmitting end transmits data through the physical channel to the receiving end, the receiving end should calculate a ratio of the received signal to noise signal power for the physical channel. At this time, the accuracy of the ratio is in close connection with an increase in an efficiency of the power control.
Since it is very difficult to accurately calculate the power of all or a portion of the signal received through a physical channel, this causes a decrease in an efficiency of the power control. Especially, if the power of the received signal is variable or the power's value is less than as usual, the power value of the received signals obtained by the receiving end becomes more inaccurate.
Also, the conventional outer loop power control has the following problems.
If the transmitting end transmits data through the physical channel to the receiving end, the receiving end measures the frame quality of frames on the physical channel frame, and adjusts the target value of a ratio of the received signal to noise signal power according to the degree of the measured frame quality. For example, the receiving end detects errors of a certain frame using a cyclic redundancy check (CRC) codes of a certain frame, and if no error exists, it judges that the frame quality of the frame is good, while if an error exists, it judges that the quality of the frame is bad.
However, if information for informing the accurate value of the quality of the frame such as the CRC is not included in the data of the frame, it is difficult to adjust the target value of a ratio of the received signal to noise signal power.